The present invention relates to a method of making prefabricated relatively rigid structural panel assemblies, such as prefabricated wall, flooring and ceiling assemblies used by the prefabricated or factory built construction industry, such as the manufactured housing industry. The panels are permanently attached to reinforcing studs, joists or trusses, forming a relatively rigid prefabricated module. Closed wall modules include a pair of parallel panels forming the wall surfaces and a plurality of transverse studs permanently attached to the wall boards.
The method of this invention is particularly, but not exclusively, adapted to a process for making such structural panel assemblies without the requirement of mechanical fasteners, such as nails, staples or screws to secure the panel to the structural members, which must be in most cases covered with batten strips. A problem with the manufacture of prefabricated wall, floor or ceiling panel assemblies has been that the components are not uniform. The boards used for studs, joists and trusses do not have a level or straight plane and may have other discrepancies, such as knot holes. The fibrous panels to which such support members are attached are somewhat flexible, but are often warped. Thus, a wall, floor or ceiling panel, which is supported by studs, joists or trusses attached by mechanical fasteners, is generally both warped and spaced from the reinforcing members in many locations. The exposed surfaces of the mechanical fasteners must also generally be covered. This is to hide fasteners popped out after construction because by inherent assembly and/or user movement and stresses resulting from the warped components. These problems can only be partially solved in "stick built" construction, where the wall, floor or ceiling panel assemblies are built entirely on site, by selection of materials, the use of shims, etc. However, factory or pre-built construction preferably utilizes mass production techniques which do not lend themselves to such hand-made adjustments.
U.S. Pat. Nos. 4,244,901 and 4,748,781, assigned to the assignee of this application, disclose methods of forming reinforced panel assemblies utilizing polyurethane foam to bond the structural support members to the panels. In the preferred embodiment, the panel is laid upon a flat support surface. The studs or support members are located on the back of the panel and clamped. A high pressure stream of a liquid foamble resin is then directed to the juncture of the support members and the panel, such that the resin foams and fills the space between the support members and the panel, permanently bonding the support members to the panel without mechanical fastening means. This method has been commercially successful in making prefabricated or factory-built structural panels; however this process is not suitable for enclosed panel construction, such as a closed wall structural assembly.
The method of this invention has advantages over the prior art and is suitable for the manufacture of enclosed panel structures, such as closed wall assemblies used by the manufactured construction industry. The disclosed method may be substantially automated and utilizes a relatively small amount of foamable resin adhesive. The method of this invention may also be used at any temperature normally encountered by the factory-built construction industry. Upon completion of the reinforced panel assembly, the assembly can be moved almost immediately using conventional mass production material handling techniques.
As stated, the method of this invention is particularly suited for the manufacture of reinforced structural fibrous panels, such as used by the manufactured construction industry for walls, floors and ceilings. The method of this invention may also be adapted for mass production techniques utilizing the materials now used by the prefabricated or factory-built construction industry.
In the method of this invention, the reinforcing members, which may be wall studs, ceiling trusses or floor joists for example, are oriented and supported vertically, such that the relatively thin side faces are located at the top of the support members. Where an enclosed structural assembly, such as a closed wall is to be manufactured, the support members are preferably first attached to one panel and the panel is supported on a horizontal surface, such that the support members extend vertically from the first panel. The support members may be attached to the first panel by the methods disclosed in the above-referenced U.S. Pat. Nos. 4,244,901 or 4,748,781. As disclosed in U.S. Pat. No. 4,748,781, the structural support members may also be metal channels.
The method of this invention then includes applying a thin bead of a thoroughly mixed two-component liquid polyurethane foamable resin adhesive axially along the top side surfaces of each of the support members. The foamable resin adhesive must have a relatively long tack time and is preferably resilient or pliable, having good wetting characteristics, green strength and fast reacting with controlled cure, such that the time that the foam remains resilient and tacky can be extended and controlled. The preferred foamable resin is of relative low viscosity and is also thixotropic, such that the resin can be thoroughly mixed in an impingement mixing chamber of an application gun, but such that the bead does not run upon application. The foam is then allowed to substantially fully cream arid rise, forming a liquid foam polyurethane bead. The support surfaces of the support members having the foamed polyurethane bead are then pressed against the panel to be joined to the support members, compressing the polyurethane beads and wetting the panel, permanently bonding the support members to the panel, without requiring mechanical fasteners. This must be completed before the polyurethane foam beads cure tack free or the polyurethane foam will not wet the surface of the panel and bond sufficiently.
In certain applications, such as where the application gun is computer controlled, it may be desirable to apply the foam bead to the panel first, rather than the support members. In such an application, the panel will be laid upon a flat support surface. A predetermined pattern of polyurethane beads are then applied to the panel with the pattern of beads corresponding to the desired locations for the support members. Where a double walled structure is to be made, the structural support members are first applied to a second panel, as described, or the support members may be supported in a fixture. The side faces of the support members are then applied to the polyurethane beads, permanently bonding the structural support members to the panel, as described.
In the most preferred method, the panel which is to be bonded to the support members is first laid upon a flat horizontal support surface. After applying the bead to the support members, the support members are turned or rotated to orient the surface having the polyurethane foam bead downwardly over the flat panel and the support surfaces are then pressed against the panel to compress the foam beads, wetting the panel surface and permanently bonding the support members to the panel. The foam beads thus fill in any imperfections or warped areas of the reinforcing support members and the panel remains flat following attachment of the support members. Further, neither the panel nor the support members are stressed during attachment and no mechanical fastening means is required.
The polyurethane foam bead is preferably applied axially along substantially the entire length of the reinforcing support members at a relatively slow forward velocity to avoid splatter and assure a good bond between the structural reinforcing members and the panel. To avoid splatter, the gun should be moved at about the forward velocity of the resin exiting the gun. A liquid resin bead having a width of about 1/4 inch applied at an application rate of less than about 3 feet per second has been found suitable for most hand applications. A two-component liquid foamable polyurethane resin adhesive is also preferred. The foamable resin adhesive should ba relatively slow acting and the formulation is preferably adjustable to accommodate the environment of the application. In the most preferred embodiment, the liquid polyurethane foamable resin begins to cream almost immediately and substantially fully rises within a few minutes, such that the foam bead is ready for bonding, as described. The foam bead must be pressed against the panel or structural member before the foam cures or the foam will not satisfactorily wet and bond sufficiently. Thus, the polyurethane foam should be formulated for the particular application. In the most preferred embodiment, the foam fully rises quickly, but the foam does not cure tack free for at least 10 minutes and may, if preferred, not cure for about 20 minutes. In most preferred applications, a polyurethane foam which cures in 15 to 20 minutes has been found to be particularly suitable for mass production applications.
The method of making a structural panel assembly of this invention is thus particularly suitable for the manufacture of prefabricated or factory-built reinforced fibrous panel assemblies, including rigid enclosed panel assemblies, such as closed wall modules used by the construction industry. A closed wall assembly may be built by the method of this invention without using mechanical fasteners or clamps and both walls may be substantially perfectly flat using mass production techniques. The reinforced wall construction may be handled using industrial mass handling techniques almost immediately upon completion of the bond and without requiring clamps. Other advantages and meritorious features of the method of this invention will be more fully understood from the following description of the preferred embodiments, the appended claims and the drawings, a brief description of which follows.